1. Field of the Invention
The present invention relates to a flexure of a disk drive suspension used for an information processor such as a personal computer, and a manufacturing method of the same.
2. Description of the Related Art
A hard disk drive (HDD) is used in an information processor such as a personal computer. The hard disk drive comprises a magnetic disk rotatable about a spindle, a carriage turnable about a pivot, etc. The carriage comprises an arm (an actuator arm), and is configured to be turned transversely relative to tracks of the disk about the pivot by a positioning motor such as a voice coil motor.
A suspension is mounted on the actuator arm. The suspension includes, for example, a load beam, and a flexure disposed to overlap the load beam. A slider, which constitutes a magnetic head, is mounted on a gimbal portion formed near a distal end of the flexure. The slider is provided with an element (transducer) for accessing data, that is, for reading or writing data. When a disk rotates, the slider is slightly lifted from a disk surface, whereupon an air bearing is formed between the disk and the slider.
In order to deal with high recording density of a disk, the hard disk drive has achieved reducing the flying height of a slider year by year. In order to stably realize a low flying height, it is extremely important to control the stiffness of a gimbal portion (around a tongue), and various means have been proposed from the past.
JP 6-203508 A (Patent Literature 1) discloses an example of a gimbal portion. The gimbal portion of Patent Literature 1 comprises a metal base made of stainless steel. By a half etching portion formed on the metal base, the stiffness of the gimbal portion is controlled. JP 9-17139 A (Patent Literature 2) discloses another example of a gimbal portion. The stiffness of the gimbal portion of Patent Literature 2 is controlled by optimizing a planar shape of a metal base.
Further, JP 11-39626 A (Patent Literature 3) also discloses an example of a gimbal portion. The gimbal portion of Patent Literature 3 comprises a pair of outriggers. At an interior of the pair of outriggers, a conductive circuit portion is arranged. By optimizing the shape of the conductive circuit portion and the shape of a metal base, the stiffness of the gimbal portion is controlled. Also, a gimbal portion disclosed in JP 2012-9111 A (Patent Literature 4) reduces the stiffness by thinning an insulating layer (base polyimide) of an unsupported conductive circuit portion.
JP 2010-67317 A (Patent Literature 5) discloses an example of a suspension substrate. In the suspension substrate of Patent Literature 5, of a plurality of conductors arranged parallel to each other, the thickness of a part of the conductors is increased and the thickness of the remainder of the conductors is reduced. As the means for forming conductors whose thicknesses are different from each other, after forming a first resist pattern having a height corresponding to a thickness of a thin conductor by a first masking process, the thin conductor (a thin copper layer) is formed by first copper plating. After that, in a second masking process, a second resist pattern for a thick conductor is formed on the first resist pattern. After that, by second copper plating which uses the second resist pattern, a thick conductor (a thick copper layer) is formed.
With conventional techniques described in Patent Literatures 1 to 3, the stiffness has been reduced by reducing the thickness of the metal base, or slimming a planar shape of the metal base. However, there is a limit to thinning or slimming of the conductive circuit portion in order to satisfy the required electrical properties. If the stiffness of the metal base is reduced, the stiffness of the gimbal portion can be reduced. However, if the stiffness of the metal base is reduced, the degree of influence that the stiffness of the conductive circuit portion relatively has over the stiffness of the gimbal portion (i.e., a stiffness contribution ratio of the conductive circuit portion) is increased. Thus, the degree of freedom of design for obtaining desired stiffness of the gimbal portion is adversely affected. Ideally, if the stiffness contribution ratio of the conductive circuit portion that affects the stiffness of the gimbal portion is zero, it is easy to optimize the stiffness of the gimbal portion.
As described in Patent Literature 4, one option of reducing the stiffness of the gimbal portion is by reducing the thickness of the insulating layer (base polyimide) of the unsupported conductive circuit portion formed around the tongue. However, partially reducing the thickness of polyimide is technically difficult. As the means for reducing the stiffness of the conductive circuit portion, one possibility is not to use a cover layer (cover polyimide) which covers a conductor. However, since the cover polyimide is as thin as several micrometers, even if the cover layer is removed, achieving sufficiently reduced stiffness cannot be accomplished.
The unsupported conductive circuit portion around the tongue does not have a metal base. For this reason, if only gold-plated conductors are used in the unsupported conductive circuit portion, it is possible to reduce the stiffness around the tongue. However, the unsupported conductive circuit portion constituted of only the conductors cannot control relative positions of the conductors which are adjacent to each other. Therefore, because of variations in the distance between the conductors, there arise problems that the electrical characteristics of the unsupported conductive circuit portion are adversely affected, and the conductors are easily deformed.
In Patent Literature 5 described above, in the conductive circuit portion comprising a plurality of conductors, one of the conductors and the other conductor are made to have different thicknesses. However, Patent Literature 5 does not relate to a technology of forming a portion having a different thickness in a longitudinal direction of a conductor. That is, in Patent Literature 5, in forming a thin conductor and a thick conductor, a first resist pattern having the same height as that of the thin conductor is formed, and a thin copper layer is formed by using the first resist pattern. After that, by overlaying a second resist pattern for forming the thick conductor on the first resist pattern, a thick copper layer is formed by using the second resist pattern. Accordingly, if the positions of the first resist pattern and the second resist pattern are deviated even if only slightly, a step portion or a discontinuous portion is formed on a side surface of the thick conductor (copper layer). Such a step portion or discontinuous portion causes the electrical or mechanical characteristics to deteriorate, and in an extreme case, the aforementioned portions may be a starting point of disconnection.